From The Collaborative International Dictionary of English v.0.48 [gcide]:
launchpad \launchpad\ n. (Rocketry)
a platform from which rockets or space craft are launched.
Syn: launching pad, launch pad, launch area, pad.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) [wn]:
launchpad
n 1: a platform from which rockets or space craft are launched
[syn: launching pad, launchpad, launch pad, {launch
area}, pad]